This invention relates to fabrication of semiconductor devices and more particularly to methods of bonding semiconductor chips to multichip modules.
Multichip modules are presently being fabricated using wire bonding or "flip chip" techniques. In the wire bonding technique, one end of a wire is bonded by thermal compression to a pad on the chip. The other end of the wire is bonded by thermal compression to a pad on the frame of the multichip carrier. Since an integrated circuit chip typically has multiple pads to which electrical connections must be made, there will be multiple wires extending from the pads on each chip to the pads disposed around the periphery of the carrier frame. As a result, the number of electrical connections which can be made between the chip and the carrier is limited by the number of pads disposed around the periphery of the die. Also, because of the space required to implement this technique, it is difficult, if not impossible to butt chips together on the carrier.
The flip chip technique, although overcoming some of the problems mentioned above in connection with the wire bonding technique is a relatively expensive technique to perform. Since this technique presently utilizes a lead/tin solder for effecting the bonds between the chip and the carrier, it is necessary to put down a barrier material to prevent the lead and tin from reacting with the aluminum pads on the chip.